The present invention relates to magnesium dichloride/alcohol adducts which are characterized by particular chemical and physical properties. The adducts of the present invention are particularly useful as precursors of catalyst components for the polymerization of olefins.
MgCl2.alcohol adducts and their use in the preparation of catalyst components for the polymerization of olefins are well known in the art.
J. C. J. Bart and W. Roovers [Journal of Material Science, 30 (1995), 2809-2820] describe the preparation of a number of MgCl2.nEtOH adducts, with n ranging from 1.4 to 6, and their characterization by means of X-ray powder diffraction. A range of allegedly new adducts, with n=6, 4.5, 4, 3.33, 2.5, 1.67, 1.50 and 1.25, is characterized in terms of X-ray diffraction pattern. According to the authors, the MgCl2.alcohol adducts can be converted to active polymerization catalyst supports through the elimination of the alcohol molecules from the adducts by thermal desolvation. In table III of the article, the characteristic diffraction lines of the above indicated new adducts are reported with reference to the interplanar distances. For convenience, the same diffraction lines are reported below with reference to the 2xcex8 diffraction angles, limited to the range of 2xcex8 diffraction angles between 5xc2x0 and 15xc2x0 (the relative intensity I/Io with respect to the most intense diffraction line is reported in parentheses). For n=1.25: 2xcex8=7.6xc2x0 (100), 12.28xc2x0 (25), 14.9xc2x0 (8); for n=1.5: 2xcex8=8.44 (100), 11.95 (48), 14.2 (46); for n=1.67: 2xcex8=6.1xc2x0 (9), 6.68xc2x0 (100), 8.95xc2x0 (50), 9.88xc2x0 (33), 11.8xc2x0 (8), 12.28xc2x0 (33), 14.5xc2x0 (13), 14.75xc2x0 (4); for n=2.5: 2xcex8=6.3 (27), 9.4xc2x0 (100), 9.93xc2x0 (70), 11.7xc2x0 (11), 12.35xc2x0 (6), 14.90 (6); for n=3.33: 2xcex8=9.14xc2x0 (15), 9.44xc2x0 (100), 11.88xc2x0 (15), 12.9xc2x0 (27); for n=4: 2xcex8=8.7xc2x0 (49), 10.1xc2x0 (73), 10.49xc2x0 (100), 11.8xc2x0 (58); for n=4.5: 2xcex8=9.65xc2x0 (100), 11.4xc2x0 (10), 12.5xc2x0 (24), 12.94xc2x0 (32), 14.25xc2x0 (20), 14.95xc2x0 (6); for n=6: 2xcex8=8.94xc2x0 (100), 13.13xc2x0 (3). A MgCl2.2EtOH.0.5H2O adduct is also reported, the diffraction lines of which in the relevant range are the following: 2xcex8=7.9xc2x0 (35); 8.5xc2x0 ( greater than 100); 9.7xc2x0 (26); 11.32xc2x0 (100); 12.59xc2x0 (11); 13.46xc2x0 (12).
Catalyst components for the polymerization of olefins, obtained by reacting MgCl2.nEtOH adducts with halogenated transition metal compounds, are described in U.S. Pat. No. 4,399,054. The adducts are prepared by emulsifying the molten adduct in an immiscible dispersing medium and quenching the emulsion in a cooling fluid to collect the adduct in the form of spherical particles. No X-ray characteristics of the adducts are reported.
U.S. Pat. No. 4,421,674 describes a method for preparing a catalyst component for the polymerization of olefins which involves the preparation of MgCl2.EtOH adducts by means of the following steps: (a) preparation of a MgCl2 solution in ethanol; (b) spray-drying said solution to collect particles of the adduct in spherical form, said adduct having from 1.5 to 20% by weight of residual alcoholic hydroxyl content and being characterized by an X-ray spectrum in which the maximum peak at 2.56 xc3x85 (i.e. 2xcex8=35xc2x0) characteristic of the crystalline anhydrous MgCl2 is practically absent and a new maximum peak at about 10.8 xc3x85 (i.e. 2xcex8=8.15xc2x0) is present; lesser peaks at about 9.16 xc3x85 (i.e. 2xcex8=9.65xc2x0) and 6.73 xc3x85 (i.e. 2xcex8=13.15xc2x0) are also reported.
EP-A-700936 describes a process for producing a solid catalyst component for the polymerization of olefins which comprises the preparation of MgCl2.EtOH adducts by means of the following steps: (A) preparation of a mixture having formula MgCl2.mROH, wherein R is an alkyl group with 1 to 10 carbon atoms and m=3.0 to 6.0; (B) spray-cooling said mixture to obtain a solid adduct having the same composition as of the starting mixture; (C) partly removing the alcohol from the above-obtained solid adduct to obtain an adduct containing from 0.4 to 2.8 mol of alcohol per mol of MgCl2. The adduct obtained in (C) is characterized by an X-ray diffraction spectrum in which a novel peak does not occur at diffraction angles 2xcex8=7 to 8xc2x0 as compared with the diffraction spectrum of the adduct obtained in (B), or even if it occurs, the intensity of the novel peak is 2.0 times or less the intensity of the highest peak present at the diffraction angles 2xcex8=8.5 to 9xc2x0 of the diffraction spectrum of the adduct obtained in (C). FIG. 2 of said European Patent Application shows a typical X-ray diffraction spectrum of the adducts prepared in (B). The highest peak occurs at 2xcex8=8.8xc2x0; two less intense peaks occur at 2xcex8=9.5 to 10xc2x0 and 2xcex8=13xc2x0, respectively. FIG. 3 shows a typical X-ray diffraction spectrum of the adducts prepared in (C). The highest peak occurs at 2xcex8=8.8xc2x0; other peaks occur at 2xcex8=6.0 to 6.5xc2x0, 2xcex8=9.5 to 10xc2x0 and 2xcex8=11 to 11.5xc2x0. FIG. 4 shows a typical X-ray diffraction spectrum of comparative adducts prepared in (C) The highest peak occurs at 2xcex8=7.6xc2x0; other peaks occur at 2xcex8=8.8xc2x0, 2xcex8=9.5 to 10xc2x0, 2xcex8=11 to 11.5xc2x0 and 2xcex8=12 to 12.5xc2x0.
A new MgCl2.alcohol adduct has now been found which is characterized by a particular X-ray diffraction spectrum, not shown by the adducts of the prior art, and/or by a particular crystallinity as shown by the Differential Scanning Calorimetry (DSC) profile of the adduct. In addition, particular MgCl2.alcohol adducts of the present invention can be characterized by their viscosity values in the molten state which, for a given alcohol content, are higher than the viscosity values of the corresponding adducts of the prior art. In addition to the alcohol, minor amounts of water can also be present in the adducts according to the invention.
The adducts of the present invention can be used to prepare catalyst components for the polymerization of olefins by reaction with transition metal compounds. Catalyst components obtained from the adducts of the present invention are capable of giving catalysts for the polymerization of olefins characterized by enhanced activity and stereospecificity with respect to the catalysts prepared from the adducts of the prior art. Also, the morphological properties of the obtained polymers are improved, particularly when adducts in spherical forms are used.
The present invention therefore relates to MgCl2.mROH.nH2O adducts, where R is a C1-C10 alkyl, 2xe2x89xa6mxe2x89xa64.2, 0xe2x89xa6nxe2x89xa60.7, characterized by an X-ray diffraction spectrum in which, in the range of 2xcex8 diffraction angles between 5xc2x0 and 15xc2x0, the three main diffraction lines are present at diffraction angles 2xcex8 of 8.8xc2x10.20, 9.4xc2x10.20 and 9.8xc2x10.20, the most intense diffraction line being the one at 2xcex8=8.8xc2x10.2xc2x0, the intensity of the other two diffraction lines being at least 0.2 times the intensity of the most intense diffraction line.
The above described diffraction pattern is unique and it has never been described in the prior art. In fact, none of the spectra reported in Bart et al. corresponds to the spectrum which characterizes the adducts of the present invention; the same applies to the adducts disclosed in EP-A-700936. As for the adducts described in U.S. Pat. No. 4,399,054, applicants repeated the preparation of the adducts according to the procedure described therein. The X-ray diffraction spectrum of the obtained adduct shows, in the range of 2xcex8 diffraction angles between 5 and 15xc2x0, the following main peaks (the relative intensity I/Io with respect to the most intense diffraction line is in parentheses): 2xcex8=8.84xc2x0 (79); 2xcex8=9.2 (100); 2xcex8=9.43 (68); 2xcex8=9.82 (19). Contrary to the adducts of the present invention, which are characterized, inter alia, by a most intense diffraction line occurring at 2xcex8=8.8xc2x10.2xc2x0, the adducts of U.S. Pat. No. 4,399,054 are characterized by a most intense diffraction line at 2xcex8=9.2xc2x0.
Preferably R is a C1-C4 alkyl, more preferably ethyl, m is between 2.2 and 3.8, more preferably between 2.5 and 3.5, n is between 0.01 and 0.6, more preferably between 0.001 and 0.4. The X-ray diffraction spectra are determined with reference to the main diffraction lines of silicon, used as an internal standard, using the apparatus and the methodology described hereinafter.
The preferred adducts of the present invention are characterized by an X-ray diffraction spectrum in which the intensity of the diffraction lines at 2xcex8=9.4xc2x0xc2x10.2xc2x0 and 9.8xc2x0xc2x10.2xc2x0 is at least 0.4 times, preferably at least 0.5 times the intensity of the most intense diffraction line at 2xcex8=8.8xc2x0xc2x10.2xc2x0.
As an alternative, or in addition to the X-ray spectrum, the adducts of the present invention are characterized by a Differential Scanning Calorimetry (DSC) profile in which no peaks are present at temperatures below 90xc2x0 C. or, even if peaks are present below said temperature, the fusion enthalpy associated with said peaks is less than 30% of the total fusion enthalpy.
The DSC analysis is carried out using the apparatus and the methodology described hereinafter.
When R is ethyl, m is between 2.5 and 3.5 and n is between 0 and 0.4, the fusion enthalpy associated with peaks possibly present at temperatures below 90xc2x0 C. is less than 10% of the total fusion enthalpy. In said case the adducts are furthermore characterized by the fact that the maximum peak occurs at temperatures between 95 and 115xc2x0 C.
Particularly preferred are adducts of the formula (I)
MgCl2.mEtOH.nH2Oxe2x80x83xe2x80x83(I) 
where m is between 2.2 and 3.8 and n is between 0.01 and 0.6, having both the above described X-ray spectrum and the above described DSC features. Adducts of this type can be further characterized by their viscosity in the molten state. In fact, it has been unexpectedly found that adducts with the above described features are also characterized by values of viscosity which, for a given alcohol content, are higher than the values of viscosity of the corresponding adducts of the prior art. In particular, on a plot of viscosity vs. EtOH molar content, the values of viscosity at 115xc2x0 C. (expressed in poise) of the adducts (I) are above the straight line passing through the points having, respectively, a viscosity/EtOH molar content of 2.43/2.38 and 1.26/3.31; at 120xc2x0 the values of viscosity of the adducts (I) are above the straight line defined by the points having viscosity/EtOH molar content values of 1.71/2.38 and 0.9/3.31; at 125xc2x0 the values of viscosity of the adducts (I) are above the straight line passing through the points defined by the viscosity/EtOH molar content values of 1.2/2.38 and 0.63/3.31.
The adducts of the present invention can be prepared with new methods, not disclosed in the prior art, which are characterized by particular modalities of reaction between MgCl2, alcohol, and optionally water.
According to one of these methods MgCl2.pROH.qH2O adducts, where R is a C1-C10 alkyl, 1xe2x89xa6pxe2x89xa66, 0xe2x89xa6qxe2x89xa61, are prepared by dispersing the particles of magnesium dichloride in an inert liquid immiscible with and chemically inert to the molten adduct, heating the system at temperature equal to or higher than the melting temperature of MgCl2.alcohol adduct and then adding the desired amount of alcohol in vapour phase. The temperature is kept at values such that the adduct is completely melted.
The molten adduct is then emulsified in a liquid medium which is immiscible with and chemically inert to it and then quenched by contacting the adduct with an inert cooling liquid, thereby obtaining the solidification of the adduct.
The liquid in which the MgCl2 is dispersed can be any liquid immiscible with and chemically inert to the molten adduct. For example, aliphatic, aromatic or cycloaliphatic hydrocarbons can be used as well as silicone oils. Aliphatic hydrocarbons such as vaseline oil are particularly preferred. After the MgCl2 particles are dispersed in the inert liquid, the mixture is heated at temperatures preferably higher than 125xc2x0 C. and more preferably at temperatures higher than 150xc2x0 C. Conveniently, the vaporized alcohol is added at a temperature equal to or lower than the temperature of the mixture. Particularly preferred products obtainable with the above specified method are the adducts of formula MgCl2.mROH.nH2O, where R is a C1-C10 alkyl, 2xe2x89xa6mxe2x89xa64.2, 0xe2x89xa6nxe2x89xa60.7, and characterized by the specified X-ray diffraction spectrum.
According to another method, the adducts of the invention are prepared by contacting MgCl2 and alcohol in the absence of the inert liquid dispersant, heating the system at the melting temperature of MgCl2-alcohol adduct or above, and maintaining said conditions so as to obtain a completely melted adduct. Said molten adduct is then emulsified in a liquid medium which is immiscible with and chemically inert to it and finally quenched by contacting the adduct with an inert cooling liquid thereby obtaining the solidification of the adduct. In particular, the adduct is preferably kept at a temperature equal to or higher than its melting temperature, under stirring conditions, for a time period equal to or greater than 10 hours, preferably from 10 to 150 hours, more preferably from 20 to 100 hours. Alternatively, in order to obtain the solidification of the adduct, a spray-cooling process of the molten adduct can be carried out.
The catalyst components obtained from the adducts obtained with the above described processes show still more improved properties over the catalyst components prepared by the adducts which have been obtained with the same preparation method but without having been maintained for the requested period of time under the described conditions.
A further method for preparing MgCl2.pROH.qH2O adducts, where R is a C1-C10 alkyl, 2xe2x89xa6pxe2x89xa66, 0xe2x89xa6qxe2x89xa61, comprises reacting the MgCl2 solid particles and vaporized alcohol in a loop reactor comprising a densified zone in which the particles flow in a densified form under the action of gravity and a fast fluidization zone where the particles flow under fast fluidization conditions. As it is known, the state of fast fluidization is obtained when the velocity of the fluidizing gas is higher than the transport velocity, and it is characterized in that the pressure gradient along the direction of transport is a monotonic function of the quantity of injected solid, for equal flow rate and density of the fluidizing gas. The terms transport velocity and fast fluidization state are well known in the art; for a definition thereof, see, for example, xe2x80x9cD. Geldart, Gas Fluidization Technology, page 155 et seqq., J.Wiley and Sons Ltd., 1986xe2x80x9d. In the second polymerization zone, where the particles flows in a densified form under the action of gravity, high values of density of the solid are reached (density of the solid=kg of solid particles per m3 of reactor occupied), which approach the bulk density of the adduct; a positive gain in pressure can thus be obtained along the direction of flow, so that it becomes possible to reintroduce the solid particles into the fast fluidization zone without the help of special mechanical means. In this way, a xe2x80x9cloopxe2x80x9d circulation is set up, which is defined by the balance of pressures between the two zones of the reactor.
In particular, the above method is suitable to prepare MgCl2.mROH.nH2O adducts, where R is a C1-C10 alkyl, 2xe2x89xa6mxe2x89xa64.2, and 0xe2x89xa6nxe2x89xa60.7, characterized by the specified X-ray diffraction spectrum, carrying out the reaction between MgCl2 particles and vaporized alcohol in the loop reactor, under conditions such that the vapour pressure of the formed adduct is kept at values lower than 30 mmHg when operating at atmospheric pressure. Preferably, the vapour pressure of the adduct is kept at values lower than 25 mmHg and more preferably in the range 10-20 mmHg.
Preferably, the reaction between magnesium dichloride and alcohol is carried out in a loop reactor in which the fast fluidization is obtained by a flow of an inert gas, such as nitrogen. The particles of the formed adduct are preferably discharged from the densified zone. As mentioned above, the reaction between magnesium dichloride and alcohol must be carried out under conditions which allow a substantial control of the reaction in order to avoid problems such as melting of the adduct or its substantial dealcoholation. Therefore, the temperature within the reactor, and particularly in the zone where the vaporized alcohol is fed, must be carefully controlled so as to maintain the vapour pressure of the adduct within the above limits. In particular, the control of the temperature is very important in view of the fact that the reaction is greatly exothermic. Therefore, it is preferred working under conditions such that heat exchange is maximized. For the same reason, the feeding of the alcohol has to be controlled in order to obtain an efficient dispersion of the alcohol in the reactor, thus avoiding the formation of the so called hot spots. The feeding of the alcohol can be carried out for example with injection nozzles, preferably located in the fast fluidization zone of the loop reactor. According to an alternative method, the alcohol can be fed to the loop reactor in a zone after the densified zone and before the fast fluidization zone, where a centrifugal mixer (of the Loedige type) is installed in order to direct the solid particles towards the walls of the reactor and create a cavitated zone where the alcohol is preferably fed. Preferably, the reactor temperature in correspondence to the alcohol feeding zone should be maintained at values in the range 40-50xc2x0 C. when operating at atmospheric pressure.
The particles of the adduct discharged from the loop reactor can be then subjected to a treatment capable of imparting them a spherical morphology. In particular, the treatment comprises subjecting the adducts to a temperature equal to or higher than the melting temperature of the adduct until the adduct is completely melted, said treatment being carried out in absence or presence of an inert liquid dispersant, then emulsifying the molten adduct in a liquid medium which is immiscible with and chemically inert to it and finally quenching the molten adduct with an inert cooling liquid thereby obtaining the solidification of the adduct in spherical form. Alternatively, in order to obtain the solidification of the adduct in spherical form, the molten adduct can be subjected to a spray-cooling process according to known techniques.
The treatment which comprises melting the adduct in the presence of an inert dispersant agent, such as vaseline oil, then emulsifying and finally quenching said molten adduct, is particularly preferred.
The liquid in which the molten adduct is emulsified is preferably a hydrocarbon liquid such as vaseline oil. The liquid used to quench the emulsion can be equal to or different from the liquid in which the molten adduct is emulsified. Preferably, it is an aliphatic hydrocarbon and more preferably a light aliphatic hydrocarbon such as pentane, hexane, heptane and the like.
The solid adducts having a spherical morphology are very suitable in the preparation of spherical catalyst components for the polymerization of olefins and in particular for the gas-phase polymerization process.
The catalyst components to be used in the polymerization of olefins comprise a transition metal compound of one of the groups IV to VI of the Periodic Table of Elements, supported on the adducts of the invention.
A method suitable for the preparation of said catalyst components, comprises the reaction between the adducts of the invention and the transition metal compound. Among transition metal compounds particularly preferred are titanium compounds of formula Ti(OR)nXy-n in which n is comprised between 0 and y; y is the valency of titanium; X is halogen and R is an alkyl radical having 1-8 carbon atoms or a COR group. Among them, particularly preferred are titanium compounds having at least one Ti-halogen bond such as titanium tetrahalides or halogenalcoholates. Preferred specific titanium compounds are TiCl3/TiCl4, Ti(OBu)4, Ti(OBu)Cl3, Ti(OBu)2Cl2, Ti(OBu)3Cl. Preferably the reaction is carried out by suspending the adduct in cold TiCl4 (generally 0xc2x0 C.); then the so obtained mixture is heated up to 80-130xc2x0 C. and kept at this temperature for 0.5-2 hours. After that the excess of TiCl4 is removed and the solid component is recovered. The treatment with TiCl4 can be carried out one or more times.
The reaction between transition metal compound and the adduct can also be carried out in the presence of an electron donor compound (internal donor) in particular when the preparation of a stereospecific catalyst for the polymerization of olefins is to be prepared. Said electron donor compound can be selected from esters, ethers, amines, silanes and ketones. In particular, the alkyl and aryl esters of mono or polycarboxylic acids such as for example esters of benzoic, phthalic and malonic acid, are preferred. Specific examples of such esters are n-butylphthalate, di-isobutylphthalate, di-n-octylphthalate, ethyl-benzoate and p-ethoxy ethyl-benzoate. Moreover, can be advantageously used also the 1,3 diethers of the formula: 
wherein RI, RII, RIII, RIV, RV and RVI equal or different to each other, are hydrogen or hydrocarbon radicals having from 1 to 18 carbon atoms, and RVII and RVIII, equal or different from each other, have the same meaning of RI-RVI except that they cannot be hydrogen; one or more of the RI-RVIII groups can be linked to form a cycle. The 1,3-diethers in which RVII and RVIII are selected from C1-C4 alkyl radicals are particularly preferred.
The electron donor compound is generally present in molar ratio with respect to the magnesium comprised between 1:4 and 1:20.
Preferably, the particles of the solid catalyst components have substantially spherical morphology and an average diameter comprised between 5 and 150 xcexcm. The term substantial spherical morphology means those particles having a ratio between the greater and smaller axis equal to or lower than 1.5 and preferably lower than 1.3.
Before the reaction with the transition metal compound, the adducts of the present invention can also be subjected to a dealcoholation treatment aimed at lowering the alcohol content and increasing the porosity of the adduct itself. The dealcoholation can be carried out according to known methodologies such as those described in EP-A-395083. Depending on the extent of the dealcoholation treatment, partially dealcoholated adducts can be obtained having an alcohol content generally ranging from 0.1 to 2.6 moles of alcohol per mole of MgCl2. After the dealcoholation treatment the adducts are reacted with the transition metal compound, according to the techniques described above, in order to obtain the solid catalyst components.
The solid catalyst components according to the present invention show a surface area (by B.E.T. method) generally between 10 and 500 m2/g and preferably between 20 and 350 m2/g, and a total porosity (by B.E.T. method) higher than 0.15 cm3/g preferably between 0.2. and 0.6 cm3/g.
Surprisingly, the catalyst components comprising the reaction product of a transition metal compound with a MgCl2-alcohol adduct which is in turn obtained by partially dealcoholating the adducts of the invention, show improved properties, particularly in terms of activity, with respect to the catalyst components prepared from the dealcoholated adducts of the prior art.
The catalyst components of the invention form catalysts for the polymerization of alpha-olefins CH2xe2x95x90CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms, by reaction with Al-alkyl compounds. The alkyl-Al compound is preferably chosen among the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEt2Cl and Al2Et3Cl3 optionally in mixture with said trialkyl aluminum compounds.
The Al/Ti ratio is higher than 1 and is generally comprised between 20 and 800.
In the case of the stereoregular polymerization of xcex1-olefins such as for example propylene and 1-butene, an electron donor compound (external donor) which can be the same or different from the compound used as internal donor can be used in the preparation of the catalysts disclosed above. In case the internal donor is an ester of a polycarboxylic acid, in particular a phthalate, the external donor is preferably selected from the silane compounds containing at least a Sixe2x80x94OR link, having the formula Ra1Rb2Si(OR3)c, where a and b are integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c) is 4; R1, R2, and R3, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms. Particularly preferred are the silicon compounds in which a is 1, b is 1, c is 2, at least one of R1 and R2 is selected from branched alkyl, cycloalkyl or aryl groups with 3-10 carbon atoms and R3 is a C1-C10 alkyl group, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane. Moreover, are also preferred the silicon compounds in which a is 0, c is 3, R2 is a branched alkyl or cycloalkyl group and R3 is methyl. Examples of such preferred silicon compounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane and thexyltrimethoxysilane.
Also the 1,3 diethers having the previously described formula can be used as external donor. However, in the case 1,3-diethers are used as internal donors, the use of an external donor can be avoided, as the stereospecificity of the catalyst is already sufficiently high.
As previously indicated the components of the invention and catalysts obtained therefrom find applications in the processes for the (co)polymerization of olefins of formula-CH2xe2x95x90CHR in which R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms.
The catalysts of the invention can be used in any of the olefin polymerization processes known in the art. They can be used for example in slurry polymerization using as diluent an inert hydrocarbon solvent, or bulk polymerization using the liquid monomer (for example propylene) as a reaction medium. Moreover, they can also be used in the polymerization process carried out in gas-phase operating in one or more fluidized or mechanically agitated bed reactors.
The polymerization is generally carried out at temperature of from 20 to 120xc2x0 C, preferably of from 40 to 80xc2x0 C. When the polymerization is carried out in gas-phase the operating pressure is generally between 0.1 and 10 MPa, preferably between 1 and 5 MPa. In the bulk polymerization the operating pressure is generally between 1 and 6 MPa preferably between 1.5 and 4 MPa.
The catalysts of the invention are very useful for preparing a broad range of polyolefin products. Specific examples of the olefinic polymers which can be prepared are: high density ethylene polymers (HDPE, having a density higher than 0.940 g/cc), comprising ethylene homopolymers and copolymers of ethylene with alpha-olefins having 3-12 carbon atoms; linear low density polyethylenes (LLDPE, having a density lower than 0.940 g/cc) and very low density and ultra low density (VLDPE and ULDPE, having a density lower than 0.920 g/cc, to 0.880 g/cc) consisting of copolymers of ethylene with one or more alpha-olefins having from 3 to 12 carbon atoms, having a mole content of units derived from the ethylene higher than 80%; isotactic polypropylenes and crystalline copolymers of propylene and ethylene and/or other alpha-olefins having a content of units derived from propylene higher than 85% by weight; copolymers of propylene and 1-butene having a content of units derived from 1-butene comprised between 1 and 40% by weight; heterophasic copolymers comprising a crystalline polypropylene matrix and an amorphous phase comprising copolymers of propylene with ethylene and or other alpha-olefins.
The following examples are given to illustrate and not to limit the invention itself.
Characterization
The properties reported below have been determined according to the following methods:
X-ray diffraction spectra were carried out with a Philips PW 1710 instrument using the CuKxcex1(xcex=1,5418) with a 40 Kv tension generator, a 20 mA current generator and a receiving slit of 0.2 mm. The X-ray diffraction patterns were recorded in the range between 2xcex8=5xc2x0 and 2xcex8=15xc2x0 with a scanning rate of 0.05xc2x0 2xcex8/10 sec. The instrument was calibrated using the ASTM 27-1402 standard for Silicon. The samples to be analyzed were closed in a polyethylene bag of 50 xcexcm thickness operating in a dry-box.
The DSC measurement were carried out with a METTLER DSC 30 instrument at a scanning rate of 5xc2x0 C./min in the range 5-125xc2x0 C. Aluminum capsules having a volume of 40 xcexcl filled with the samples in a dry-box were used in order to avoid hydration of the samples.
The viscosity measurement were carried out according to ASTM D445-65 using a Cannon-Fenske type viscosimeter. During the measurement the samples are maintained in a dry nitrogen environment in order to avoid hydration.